In mobile networks, such as a 3GPP (Third Generation Partnership Project) mobile network, various types of terminal devices may be used. For example, Machine Type Communication (MTC) terminal devices may be used in addition to conventional types of terminal devices, such as mobile phones, smartphones, data modems, mobile computers, or the like. In the following a terminal device of any type may also be termed as user equipment (UE). MTC terminal devices typically transmit and receive only small amounts of data, which may occur more or less infrequently, e.g., once per week to once per minute. MTC terminal devices may also be polled for data, resulting in an irregular pattern of data transmission. MTC terminal devices are typically assumed to be autonomous sensor devices, alarm devices, actuator devices, remote control devices, or the like, which communicate with application servers, rather than being used for communication by a human user. Hence, this type of communication may also be referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). An application server may in turn configure the MTC terminal device and receive data from them. The application server may be within or outside the mobile network.
Considering the above, MTC terminal devices are typically characterized by a modest bit rate and sparse communication. MTC terminal devices may therefore be implemented with low-performance data transmission capabilities. Further, MTC devices typically need to be very energy efficient, since external power supplies may not be available and/or it may be practically or economically not feasible to frequently replace or recharge their batteries.
A known way of energy saving in a UE, which may also be applied to MTC devices, is to use Discontinuous Reception (DRX). By means of DRX, a UE can enter an energy efficient sleep mode when no data transmission is needed. In the sleep mode receiver circuitry of the UE may be turned off. DRX can be used in idle mode or in connected mode.
However, using DRX in idle mode requires a UE to re-establish its connection to the mobile network every time it needs to transmit some data. This may cause undesirable signaling overhead and also excessively consume energy in the UE. Such idle-to connected mode transitions and associated signaling can be avoided by using DRX in connected mode. However, keeping a large number of UEs in connected mode may require a significant amount of resources of an uplink (UL) control channel, e.g., of the Physical UL Control Channel (PUCCH) as used in 3GPP LTE (Long Term Evolution).
The UL control channel may be used for supporting efficient connected mode operation. For example, the UE may use allocated resources of the UL control channel for scheduling requests, i.e., requests for resources for UL transmissions. Further, the UL control channel may also be used for reporting channel conditions, e.g., in terms of a Channel Quality Indicator (CQI), or for providing feedback of a retransmission protocol, e.g., of a Hybrid Automatic Repeat Request (HARQ) protocol, with respect to downlink (DL) transmissions.
Accordingly, there is a need for techniques which allow for efficiently maintaining a connection to multiple terminal devices.